Gas turbines are increasingly subject to the strict environmental protection regulations of many countries with regard to exhaust gas composition. In operating a gas turbine, the maintenance of the regulations on the maximum permitted NO.sub.x emissions, more than anything else, causes great difficulties. Thus there are currently legal regulations in force, namely in the U.S.A., whereby the NO.sub.x emissions content may not exceed 75 ppm at 15 Vol. % O.sub.2. Similar regulations have to be observed in most industrial states and it is rather to be expected that the permissible figures will in future be corrected in a downwards direction. Up to now, these requirements could only be maintained by the use of large injections of water or steam into the combustion space. The means used for the reduction of the emission figures, i.e. water or steam, do, however, introduce some important disadvantages.
If water is injected into the combustion space, a loss of efficiency is to be expected. In addition, water is not always and everywhere available in sufficient quantities, for example in low precipitation countries. The water must also be subjected to a preparation process before its use because many minerals appearing in the water, for example sodium, common salt, etc., have a strongly corrosive effect on their environment. This preparation process is, in this context, costly and energy intensive. If, on the other hand, steam is introduced to the combustion space, the loss in efficiency mentioned above is thus avoided. The steam generation, however, also presupposes water and its preparation is not less energy intensive.
A combustion chamber of the type mentioned above without water or steam injection is known from German Application 2,950,535 which corresponds to European Patent Application No. 29619. Due to the fact that a premixing/preevaporation process takes place between the injected fuel and the compressor air at a large excess air coefficient and within a number of tubular elements before the actual combustion process takes place downstream of a flame holder, the emission figures of pollutants from the combustion can be substantially reduced. The combustion with the greatest possible excess air coefficient--fixed on the one hand by the flame continuing to burn at all and, on the other, by not too much CO occurring--reduces, however, not only the pollutant quantity of NO.sub.x but also effects a consistent restriction of other pollutants, namely, as already mentioned, of CO and of unburned hydrocarbons, to low levels. This optimisation process can, with the known combustion chamber, be forced in the direction of still lower NO.sub.x values by keeping the space for combustion and subsequent reactions much longer than would be necessary for the actual combustion. This permits the choice of a larger excess air coefficient, with, in fact, larger quantities of CO occurring initially but these can further react to CO.sub.2 so that the CO emissions finally remain small. On the other hand, however, only a small amount of additional NO forms because of the large air excess. Since several tubular elements undertake the premixing/pre-evaporation, only enough elements are operated with fuel in the load control operation in each case so that the optimum excess air coefficient is obtained for the current operating phase (start-up, part load, etc.).
Now such a type of combustion chamber has, however, the shortcoming that, particularly at part load, i.e. when only a part of the elements are in operation with fuel, the limit of flame stability is met because the extinguishing limit is attained, even at an excess air coefficient of approximately 2.0, because of the very weak mixture and the resulting low flame temperature.